The present invention relates to magnetic shields for use in or about television picture tubes, or like configured, light gauge parts. In order to be operable, a picture tube must include a low to no carbon magnetic shield positioned adjacent the outwardly and forwardly sloping picture tube walls. Such magnetic shields prevent external magnetism from distorting the television picture.
These shields are made of a very thin low to no carbon steel. The material is approximately 0.004 inch thick. Such shields are usually formed by blanking, drawing and then trimming a very thin piece of steel.
Unfortunately, it is difficult to form such thin steel without creating wrinkles. Also, more expensive drawable steel is required. This method also restricts design of the shield and of the resulting picture tube in that a draw flange must be provided on the shield.
FIG. 1 shows a prior art magnetic shield with, as is typical, numerous wrinkles and creases. Such shields have usually been placed inside the tube because of their poor appearance, even though such interior placement is not functionally necessary. The wrinkles and creases hold dirt, moisture and fluid used to degrease the part after forming. If such dirt, moisture or fluid gets inside the picture tube, it will cause discrepancies in the quality of the picture. Foreign matter can also short the guns.
Elaborate steps are sometimes taken to try to shake dirt and fluid out of such magnetic shields. They are typically cleaned and then placed on a shaker table to shake dirt and fluid out of the wrinkles and creases.
In spite of precautions, dirt in the magnetic shield is still one of the causes of tube failure. Manufacturers of picture tubes have had a long felt need for wrinkle-free magnetic shields which would substantially eliminate the foregoing contamination and cosmetic problems.